Provider works more or less now.

lib/provider.js

@@ -1,8 +1,12 @@
+var path = require('path')
+var fork = require('child_process').fork
+
 var adb = require('adbkit')
 var async = require('async')
 
 var log = require('./util/logger').createLogger('provider')
 var client = adb.createClient()
+var workers = {}
 
 client.trackDevices(function(err, tracker) {
   if (err) {
@@ -14,13 +18,117 @@ client.trackDevices(function(err, tracker) {
 
   tracker.on('add', function(device) {
     log.info('Found device "%s" (%s)', device.id, device.type)
+    maybeConnect(device)
   })
 
   tracker.on('change', function(device) {
     log.info('Device "%s" is now "%s"', device.id, device.type)
+    maybeConnect(device) || maybeDisconnect(device)
   })
 
   tracker.on('remove', function(device) {
     log.info('Lost device "%s" (%s)', device.id, device.type)
+    maybeDisconnect(device)
   })
 })
+
+function isConnectable(device) {
+  switch (device.type) {
+    case 'device':
+    case 'emulator':
+      return true
+    default:
+      return false
+  }
+}
+
+function isConnected(device) {
+  return workers[device.id] && workers[device.id].proc
+}
+
+function maybeConnect(device) {
+  if (isConnectable(device) && !isConnected(device)) {
+    log.debug('Spawning worker for device "%s"', device.id)
+    var proc = fork(path.join(__dirname, 'device'), {
+      env: {
+        ANDROID_SERIAL: device.id
+      }
+    })
+    proc.on('error', function(err) {
+      log.error('Worker of device "%s" had an error: %s',
+        device.id, err.message)
+    })
+    proc.on('exit', function(code, signal) {
+      var data = workers[device.id]
+      delete workers[device.id]
+      if (code === 0) {
+        log.info('Worker of device "%s" stopped cleanly', device.id)
+      }
+      else {
+        log.error('Worker of device "%s" had a dirty exit', device.id)
+        if (Date.now() - data.started < 10000) {
+          log.error('Worker of device "%s" failed in less than 10 seconds,' +
+            ' will not attempt to restart', device.id)
+        }
+        else {
+          log.info('Restarting worker of "%s"', device.id)
+          maybeConnect(device)
+        }
+      }
+    })
+    workers[device.id] = {
+      device: device
+    , proc: proc
+    , started: Date.now()
+    }
+    return true
+  }
+  return false
+}
+
+function maybeDisconnect(device) {
+  if (isConnected(device)) {
+    log.info('Releasing worker of %s', device.id)
+    gracefullyKillWorker(device.id, function() { /* noop */ })
+    return true
+  }
+  return false
+}
+
+function gracefullyKillWorker(id, done) {
+  var proc = workers[id]
+    , timer
+
+  timer = setTimeout(function() {
+    log.error('Worker of "%s" did not stop in time', id)
+    proc.removeListener('exit', onExit)
+    proc.kill('SIGKILL')
+    done()
+  }, 10000)
+
+  function onExit() {
+    clearTimeout(timer)
+    done()
+  }
+
+  proc.once('exit', onExit)
+  proc.kill('SIGTERM')
+}
+
+function gracefullyExit() {
+  log.info('Stopping all workers')
+  async.each(Object.keys(workers), gracefullyKillWorker, function(err) {
+    log.info('All cleaned up')
+    process.exit(0)
+  })
+}
+
+process.on('SIGINT', function(e) {
+  log.debug('Received SIGINT')
+  gracefullyExit()
+})
+
+process.on('SIGTERM', function(e) {
+  log.debug('Received SIGTERM')
+  gracefullyExit()
+})